The invention relates to improvements in rolls which can be used in calenders or in analogous machines to heat or cool running webs of paper or the like. More particularly, the invention relates to improvements in rolls of the type wherein a rotary shell surrounds and is centered on a stationary carrier and has a peripheral surface which cooperates with the peripheral surface of an identical or different roll to define a nip for the passage of a running web of paper, textile material, metallic or plastic foil or a composite web having two or more overlapping layers of paper and/or other sheet material.
Published German patent application Serial No. 38 38 726 discloses a roll having a rotary shell which can be used to heat or cool a running web of paper or the like. The shell is rotatable around a stationary carrier and is rotatably journalled on the carrier by one or more supporting elements and is provided with axially parallel bores which are adjacent to its peripheral surface and can be used to convey streams or flows of a heating or cooling fluid. Heating or cooling fluid is supplied and evacuated through a space between the peripheral surface of the stationary carrier and the internal surface of the shell, and through one or more bores in the carrier. A drawback of the just described roll is that it does not permit highly predictable and accurate cooling or heating of the end portions of the shell. Consequently, the heating or cooling system of such roll cannot reliably prevent the development of the so-called oxbow effect which involves deformation of end portions of the rotary shell. This, in turn, affects the quality of the marginal portions of the running web. Thus, the luster and/or smoothness of the marginal portions of the treated web is likely to be less than satisfactory and the thickness of such marginal portions is likely to fluctuate within a rather wide range.
German Pat. No. 30 14 891 discloses a roll employing a rotary shell and a displacing element which latter is confined in the shell. The patent proposes to solve the problem of adequately influencing the temperature of the end portions of the shell (i.e., of the marginal portions of a web which is being treated as a result of contact with such shell) by utilizing two heat carrying fluid streams which are maintained at different temperatures. A drawback of the patented roll is that its initial cost and its maintenance cost are rather high. Furthermore, it is difficult to adequately (predictably) mix the two fluid streams in an annular space between the external surface of the confined displacing element and the internal surface of the shell.
German Utility Model No. 90 14 117.2 discloses a roll wherein the temperature of the rotary shell can be influenced by conveying a fluid medium through axially parallel channels which are adjacent the peripheral surface of the shell and alternate with axially parallel channels for evacuation of spent fluid medium. The Utility Model further proposes the utilization of a distributor which is installed at one end portion of the shell and comprises means for directing freshly supplied fluid medium as well as spent medium into selected channels at the periphery of the shell. A drawback of the just outlined roll is that it cannot heat or cool the marginal portions of a running web with a requisite degree of reliability.
German Auslegeschrift No. 1 244 097 proposes a roll having a shell whose peripheral surface can be heated by a pressurized fluid. Such fluid is confined in a chamber which is directly surrounded in part by a stationary carrier for the shell, in part by a stationary cylinder which is installed between the carrier and the shell, and in part by a set of pipes which are recessed into the core and are overlapped by sealing strips received in the recesses of the carrier. The roll which is disclosed by this publication is complex and expensive and cannot ensure reliable and reproducible heating of each and every portion of a running web of paper or any other material contacting the peripheral surface of the shell.
Published German patent application Serial No. 1 952 900 discloses a roll adapted to be heated by oil which is admitted into and is evacuated from the roll through axially disposed inlet/outlet means. The relatively thin shell of the roll surrounds a rotary core and defines with the latter a helical channel for the flow of heating fluid. The channel receives fresh fluid from and discharges spent fluid into radially extending bores of the core. The just described roll is expensive and is not capable of ensuring highly accurate heating or cooling of the marginal portions of a running web of paper or the like.
German patent No. 31 40 425 discloses a heatable roll wherein the end portions of a rotary shell are connected with two separately produced sleeves serving as a means for admitting fresh heating fluid into and for evacuating spent heating fluid from an annular clearance which is defined in part by a displacing element in the shell. The patented roll exhibits the same drawbacks as the previously described conventional rolls.
Published German patent application Serial No. 39 25 367 discloses a roll which is used to treat running webs as a result of the application of heat and pressure. The rotary shell of the roll is provided with axially parallel channels for the flow of a heating medium close to the peripheral surface of the shell from and into bores which are machined into the stationary core for the shell. A drawback of such roll is that it cannot ensure adequate heating or cooling of the end portions of the shell.